1. Field of the Invention
The present invention relates to computing devices and, more particularly, to computing devices having external caches.
2. Description of the Related Art
Conventionally, portable computer systems often use power management techniques to place a microprocessor in a lower power mode when the computer system is idle or otherwise has a low processing demand. It is also known that other subsystems of portable computer systems can likewise be placed in low power modes.
Today, conventional portable computer systems often includes an internal cache memory and an external cache memory. The internal cache memory is often integrated into the microprocessor chip, while the external cache memory is typically a separate chip. The internal cache memory is also known as a primary cache memory, and the external cache memory is also known as a secondary cache memory. Conventionally, when the microprocessor enters a low power mode, the entire microprocessor chip including the internal cache memory enters the low power mode. The external cache memory is normally not power managed; hence, it always remains in the normal power mode. However, to save additional power, the computer system can also place the external cache subsystem in a low power mode. U.S. Pat. No. 5,632,038 describes a secondary cache memory system that is turned off when the processor of the computer system is determined to be inactive. A control register is used by the microprocessor to inform a cache controller on how to control the secondary cache memory system.
Computer systems often function in control loops to control operation of the computer systems. The control loops include an event loop and an idle loop. The event loop monitors the computer system for events and upon receiving an event causes the event to be processed. The idle loop is used by the computer system when there are no events for the event loop to process. The microprocessor for the computer system is placed in the low power mode upon entering the idle loop where small amounts of processing for administrative and background matters are performed. Thus, the computer system enters the idle loop to reduce power consumption.
One problem of the conventional approaches is that efficient power management of external cache memories has not been provided in a manner suitable for use in idle loops. Conventional idle loops are also not equipped to facilitate power management of external cache memories.
Thus, there is a need for more robust techniques for managing power consumption by an external cache of a computer system.